"It could turn out that making dramatic changes in each of these areas could prove ... untenable, or politically impossible. Yet we have no choice but to take a very close look and see how we can do all of this better," Hagel said.
Hagel has already generated some political capital among congressional Republicans since his contentious Senate confirmation hearings earlier this year.
"Many of the measures he recommends . . . are long overdue and should be executed absent the military's current resource crisis," McKeon said in a statement on Wednesday. "I look forward to working with Secretary Hagel to reform these institutions."
But during his speech, Hagel indicated he would be willing to burn some of that goodwill among Republicans in Congress to move the Pentagon toward his vision for the future.
DOD leaders need to "be steely-eyed and clear-headed in our analysis, and explore the full range of options for implementing our national security strategy," no matter how hard congressional lawmakers battle against those proposals, he said.
"We need to challenge all past assumptions, and we need to put everything on the table."
Hagel is already spearheading a review of the White House's national security strategy focused on the Asia-Pacific region unveiled last February.
That ongoing review would look at necessary changes to the Pentagon’s strategy, force posture and investments to cope with the massive, across-the-board cuts stemming from the administration's sequestration plan.
With sequestration, $41 billion will be cut in 2013 and $500 billion could be reduced in the next decade, which senior military leaders have said would require the Pentagon to change its new strategy and scale back ambitions.
Along with that review, Hagel announced plans to begin "close scrutiny" of the department's hierarchy and how its forces are distributed across the globe, "most of which date back to the early years of the Cold War."
"Operational forces of the military ... have shrunk dramatically since the Cold War era," Hagel noted. "Yet the ... command and support structures sitting atop these smaller fighting forces have stayed intact."
That situation has resulted in wasted spending on manpower and infrastructure that could have been used elsewhere in the Pentagon, he said.
Trimming those excess bases and command structures will not diminish America's ability to meet its national security challenges, since most of the world's future conflicts will not be determined by military power alone, according to Hagel.
"Most of the pressing security challenges today have important political, economic, and cultural components, and do not necessarily lend themselves to being resolved by conventional military strength," he said.
But cutting military bases and facilities that have stood since the Cold War will force the DOD to cross a tough political line when Hagel makes his case for those cuts to Congress.
That said, the "principled realism" guiding Hagel's strategy going forward is already beginning to resonate with officials inside the Pentagon, and should do the same on Capitol Hill.
"Since 9/11, the military has grown more deployable, more expeditionary, more flexible, more lethal, and more professional," Hagel said.
"The task ahead for the Department is to prepare for the future, but not in a way that neglects, or is oblivious to, the realities of the present," he added.
--updated at 4:02pm